The peculiar velocities of local type Ia supernovae and their impact on cosmology

We quantify the effect of Type Ia supernova (SN Ia) peculiar velocities on the derivation of cosmological parameters. The published distant and local SNe Ia used for the Supernova Legacy Survey first-year cosmology report form the sample for this study. While previous work has assumed that the local SNe are at rest in the CMB frame (the no-flow assumption), we test this assumption by applying peculiar velocity corrections to the local SNe using three different flow models. The models are based on the IRAS PSCz galaxy redshift survey, have varying beta = Omega(0.6)(m)/b, and reproduce the Local Group motion in the CMB frame. These data sets are then fit for w, Omega(m), and Omega(A) using flatness or LCDM and a BAO prior, and the chi(2) statistic is used to examine the effect 2 of the velocity corrections on the quality of the fits. The most favored model is the model, which produces a fit significantly better than the no-flow assumption, consistent with previous peculiar velocity studies. By comparing the no-flow assumption with the favored models, we derive the largest potential systematic error in w caused by ignoring peculiar velocities, Delta w = +0.04 For Omega(A) the potential error is Delta Omega(A) = -0.04 and for Omega(m) the potential error is. Delta Omega(m) < +0.01. The favored flow model (beta = 0.5) produces the following cosmological parameters: w = -1.08(-0.08)(+0.09), Omega(m) = 0.27(-0.02)(+0.02) assuming a flat cosmology, and Omega(A) = 0.08(-0.07)(+0.08) and Omega(m) = 0.27(-0.02)(+0.02) for a w = -1 (ACDM) cosmology.